Technical Field
The present disclosure relates to control systems and more particularly to systems for controlling the pressure within an apparatus used to test pressure measuring instruments.
Description of the Related Art
A pressure measuring instrument may be tested by fluidly coupling the pressure measuring instrument to a pressure comparator. A highly accurate reference pressure gauge also is fluidly coupled to the pressure comparator. A pump within the pressure comparator is used to develop a predetermined pressure within a chamber of the pressure comparator. To determine the accuracy of the pressure measuring instrument, a pressure measured by the pressure measuring instrument is compared to a pressure measured by the reference pressure gauge. Typically, this process is repeated for a plurality of predetermined pressures within a range of pressures for which the pressure measuring instrument is rated to measure. For example, if the pressure measuring instrument is rated to measure a maximum pressure of 300 pounds per square inch (psi), the predetermined pressures may include 15 psi, 30 psi, 60 psi, 150 psi, and 300 psi, which correspond to 5%, 10%, 20%, 50%, and 100% of the maximum pressure value, respectively.
A conventional pressure comparator may include an electric pump that is used to develop pressure within a chamber of the pressure comparator and a first lever coupled to a switch that can turn the pump on and off. While the first lever is at a first position, the switch is open and no power is provided to the pump and, thus, the pump does not operate. While the first lever is at a second position, the switch is closed and power is provided to the pump and, thus, the pump operates to increase or decrease the pressure within the chamber. That is, in a conventional pressure comparator, either no power or full power is provided to the pump depending on whether the first lever is at the first position or the second position. While full power is provided to the pump, the pump operates at its maximum capacity. The conventional pressure comparator also includes a second lever that is coupled to a bleed valve, which is coupled to the chamber. While the second lever is at a first position, the bleed valve is closed. While the second lever is at a second position, the bleed valve is open, which causes the pressure within the chamber to change slowly.
Typically, an operator of the conventional pressure comparator turns the pump on by moving the first lever from the first position to the second position while watching a display of the reference pressure gauge. After the pressure measured by the reference pressure gauge exceeds a set point (e.g., 50% of the maximum rated pressure of the pressure measuring instrument being tested), the operator turns the pump off by moving the first lever from the second position to the first position. Then, while watching the display of the reference pressure gauge, the operator moves the second lever from the first position to the second position, which causes the pressure within the chamber to decrease slowly. When the pressure measured by the reference pressure gauge is approximately equal to the set point, the operator closes the bleed valve by moving the second lever from the second position to the first position. The operator then turns a knob to adjust the position of a piston within a Vernier chamber, which causes the pressure within the chamber to change very slightly until the pressure measured by the reference pressure gauge is equal to the set point. The operator then compares the pressure measured by the pressure measuring instrument being tested to the pressure measured by the reference pressure gauge. If the pressure measured by the pressure measuring instrument is not equal to the pressure measured by the reference pressure gauge, the operator may calibrate the pressure measuring instrument so that the pressure measured by the pressure measuring instrument is equal to the pressure measured by the reference pressure gauge
Because the pump of the conventional pressure comparator is either not operating or operating at full capacity, it can be difficult for the operator to accurately set the initial pressure within the chamber of the pressure comparator. For example, if the operator is attempting to set the pressure within the chamber to a set point corresponding to 5% of the maximum rated pressure of the pressure measuring instrument being tested, moving the first lever from the first position to the second position for a short period of time may cause the pressure within the chamber to exceed 10% of the maximum rated pressure of the pressure measuring instrument being tested. The operator then has to move the second lever to open the bleed valve and wait for the pressure to decrease to 5% of the maximum rated pressure, which can be time consuming. The operator must be mindful of which lever she is moving. If the operator intends to move the second lever, but accidentally moves the first lever, the pressure within the chamber is increased instead of decreased. The operator must then operate the second lever for a relatively long period of time to cause the pressure within the chamber to decrease to the set point.
Accordingly, there is a need for an apparatus that can be used to set the pressure within a chamber more quickly and easily.